1. Field of the Invention
The present invention relates to a thermosensitive stencil paper for printing, which comprises a porous tissue paper and a thermoplastic resin layer formed thereon, and more particularly to a thermosensitive stencil paper having excellent printing-resistance, capable of producing high quality images with high resolution.
2. Discussion of Background
Conventional thermosensitive stencil paper is prepared by attaching a thermoplastic resin film to a porous substrate such as a porous tissue paper with an adhesive, for example, a pressure-sensitive adhesive, or providing a thermoplastic polymer layer on one side of a porous substrate such as a porous tissue paper.
To make a printing master using the above-mentioned thermosensitive stencil paper, an original is caused to adhere closely to the thermoplastic resin film or the thermoplastic polymer layer of the thermosensitive stencil paper, and infrared rays or light from a xenon flash tube is applied to the porous substrate side of the thermosensitive stencil paper to generate thermal energy at solid image areas of the original. In the thermoplastic resin film or thermoplastic polymer layer, the areas corresponding to the solid image areas of the original which closely adheres to the above resin film or polymer layer are melted by the thermal energy and the porous substrate is exposed at these areas. Thereafter, the original is peeled from the thermosensitive stencil paper to prepare the printing master.
Alternatively, while images formed on the original are read by an image sensor, the thermoplastic resin film or thermoplastic polymer layer of the thermosensitive stencil paper which closely adheres to the original is partially melted to correspond to the solid image areas on the original by the application of the thermal energy from a thermal head.
The thermosensitive stencil paper thus prepared is wound around a printing drum and printing ink is applied thereto from the porous substrate side to be ready for printing.
In the case where the thermoplastic resin film or thermoplastic polymer layer of the thermosensitive stencil paper is partially melted by using the thermal head, part of the melted film or polymer disadvantageously adheres to the surface of the thermal head, which impairs the printing master. Thus, the thermal head needs cleaning periodically. This cleaning operation, however, makes the process for making a printing master more complicated.
There is proposed a thermosensitive stencil paper in which an overcoat layer is formed on a thermoplastic resin film in order to prevent the thermoplastic resin film from sticking to the thermal head during the preparation of a printing master. Unfavorably, however, while thermosensitive stencil papers of that kind are allowed to stand for a while with the substrate of one stencil paper being superimposed on the overcoat layer of the other stencil paper, the resin contained in the overcoat layer migrates to the substrate overlaid thereon, and the desired effect of the overcoat layer cannot be accomplished.
To solve the above problem, various surface-treated thermoplastic resin films for the thermosensitive stencil paper have been developed. For instance, a thermoplastic resin film with a center-line mean roughness (Ra) measured in accordance with JIS B 0601 of 0.01 to 0.3 .mu.m is disclosed in Japanese Laid-Open Patent Application 1-168494, and embossed films for the thermosensitive stencil paper are disclosed in Japanese Laid-Open Patent Applications 51-499 and 51-163598. However, such surface-treated films cannot completely solve the above problem at the present stage.